event participant listing report: fee amount empty when additional registrant

create an event and enable multiple registrant listings
configure fee options using a priceset
register and individual with additional registrants
run the participant listing report, enabling the fee amount field

result: the primary registrant will have the amount field displayed; the additional registrants will not

issue: the fee amount is being pulled directly from the _participant table. that column is populated for the primary registrant, but NULL for the additional registrants. the additional registrant fees are found in the line_item table

questions: I suspect that the presence of the fee in the participant table is left over from the old fee structures (prior to the accounting work when all fees were moved to the price_item and line_item structures). it's just happens that it "seems" to work for the primary registrant. I think we probably want to be pulling the fees from the line_item table and calculating the total for display in this report.

but I'm a little uncertain if that's the desired structure.